Cam Lobe Centers

[RockCrusher]

[74 Thing]

Give them a call...
http://www.rdvalvespring.com/index.html

or you can call Joel Mohr too he uses the beehive springs from them as well.

[RockCrusher]

[Ken Taber]

I am runnign what R&D Spring calls his ford modular single bee hives on the heads I mentioned in my eariler post and they are the cats ass up to just uder 7000 rpm ,

[Steve Arndt]

[RockCrusher]

Yeah Steve, you're right about the delicate guides after cutting for duals. I'd like to see someone come out with a couple good beehive setups for VW's so most of the time we don't need to cut like that.
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[steve34]

I just finished porting my new 043 casting 42 by 37.7 heads. I cut them for dual springs too. Now I am regretting this. It basically ruins the head for new guids in the future, unless you are super careful removing the guides.

I think my next heads will be single spring with an Engle 100 cam set at 9.5 to 1. For the Oregon dunes etc.

I will se how this new motor likes the duals.

I have used dual springs several times before. Hopefully the guide bosses dont crack and the heads last several years. I am looking at hitting St. Anthonys this summer.

[modok]

I hope nobody takes me too serious, I'm still trying to figure it all out myself you know. haha
Ken, feel free to post here any time, I do look forward to hearing about what you guys are up to.

[Ken Taber]

Modok , I envy you and your ability for applying theory. I have a very limited knowledge of theory, I talk with friends like Joe Mohre , Clyde Berg and Doug Berg who is working with me in my shop , Don at Rand D Spring and I try different cams and change specks and see what happens. I am soon going to be dynoing a 1915 duel spark plug 46X37.5 wedge port head with 11.5 c/r Engle fk-46 intake fk-45 exhaust , this is baised on what Jake Rabe has done. Oh the cam is on a 102 lobe center.

[modok]

[modok]

I'll try to build a better rule based on existing ones

At idle and lower rpms the "dynamic compression" or more properly the calculated 'cranking compression" theory is quite true. How much volume in the cylinder when the valve closes is all there is to it. If you have a late IC point much of the charge will be pumped back out again before the valve closes and that reduces VE at those speeds.
As the rpm rises and port velocity begins to come up the rules change; the length of the intake stores momentum and the intake will continue charging after the piston stops and turns around at BDC. The thing is without airspeed, this does not happen; no speed=no momentum.
So, what rpm the engine starts to defy the cranking compression theory is related to how the ports and runners are sized. Smaller brings the airspeed up sooner.
Once the airspeed is up the intake contines to flow till it runs out of momentum, then it STOPS, and then it starts flowing backwards.
How strong it does this and how it is timed is related to the intake diameter and length.
With a late IC there is a lot of time for it to flow backwards at lower speeds.

Around peak torque, if the intake diameter and length and cam are within reason, the intake valve will be closing right around the time the intake is STOPED not flowing forwards or backwards, that is why I say moving the IC point a few degrees one way or the other has no big effect on peak torque most cases.

Past peak torque the intake is still trying to flow as the intake valve is closing, so delaying the IC point helps performance past peak torque and at the higher rpms, as everybody knows.

So by mashing three or four rules of thumb together....... I have created a monster? or is that helpful!

[Ken Taber]

Modok if your engine size is up to 2300 stay with a 1 1/2" exhaust , if you go bigger then 1/5/8 is what you want. This is for a torquer only. These motors are the most forgiving things to drive. I have to admit that I have had my Stucka dyno since 1974 and it was not until 2003 that I put this torque combo together and found out that you could put a full load on the water brake at 1000 rpm and watch it make 21 hp and 110 lbs of torque.

[58 Plastic Tub]

Gentlemen- you're 75% of the way there. But the last 25% is universally acknowledged to be the most importation station of the cross.

As far as the thread being too technical... I'm unbelievably tired of threads in the "performance- engines/transmissions" section of this site that have nothing to do with performance, or engines, or transmissions.

Perhaps this is too much for the average Sambista, but I'm getting a handle on something that I've never understood.

PLEASE finish this up for me.
_________________
Stan Galat
"A single point in isolation is a reference point. Two points is a line. Three points is a trend. Trends don't lie."

[modok]

yeah, it's impossible really because nothing is true 100% of the time.
i spose all you need to know is enough to form a hypothesis, make a cam to test it, and see if you are right. If you cut the back off the car or have a buggy a cam change can be done in about two or 3 hours.

[RockCrusher]

Problem here Modok is you're trying to write a cam book and it will just confuse most people. I think it is enough to give folks an idea of how everything inter-relates. After that it gets way too theoretical and every minor question that's asked leads to another long dissertation.

I'm not trying to with-hold info but what you took years to learn and understand can't be taught in a forum thread. THAT is why most people need a good engine builder or have to rely on the "W-120 always worked well for me" crowd.

RC
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[modok]

That is amazing Ken, i never built anything like that
Could i ask what you using for headers with that setup?

[Ken Taber]

!st off I meant the change from 108 to 100 is a lobe center change. Engle is not correct when they told you that going from 108 to 106 lobe centers whould move hp from 6500 to 6000 rpm. They told me the same thing and my dyno proved it took an 8 degree change to move it that much. I'll bet none of you have ever seen a motor of 2300 or bigger pull a full load at 1000 rpm on a dyno with a cam like fk-43, well you can do it if the lobe center is 100. They are all done by 6000 but the torque curve is almost flat.

[modok]

My fingers are tired, maybe somebody elso do it.......
Really does just what most people say.
I've heard that each degree you move it shifts the prm range up/down 100 rpm. kinda true

Another somewhat true rule of thumb is, within reason of course, is that extending the IC point will help performance above peak torque while losing performance below peak torque. But peak torque will be the same if it is the only thing you change.

Where peak torque is, is usually all about the intake; sizing the port and valve to the engine will be the biggest factor in where peak torque is.

[58 Plastic Tub]

Thank you.

You said intake closing was the most important point. An explanation?
_________________
Stan Galat
"A single point in isolation is a reference point. Two points is a line. Three points is a trend. Trends don't lie."

[modok]

The exhaust will close 3 degrees later
EC is a more critical point. Now you have three degrees more time for the exhaust to keep flowing after the piston has come up, or three degrees more time for the exhaust to flow backwards into the cylinder and intake port(not good). when you close the exhaust valve is a lot more critical than when you open it. At what rpm it is good and bad depends once again on the valve/port/header combo. If an engine is near the top of the rpm range and running near the limit of it's exhaust flow, having the valve open a few extra degrees after the piston comes up can really help, but if the engine has more than enough flow for the rpms it's running you won't see any gain from this alone.

The intake opens three degrees sooner
One thing about the intake stroke is it's MAIN part is when the piston is going fastest, the highest piston speed is at like 80 degrees ATDC, while the highest valve lift is like 100-110(intake lobe centerline). So you might say it's the cam little late by nature. The sooner you start lifting the valve the higher it will be when the pistons is goin', and that can be a good thing for perfomance all around. So you do want to lift the valve as soon as you can without getting into trouble. The trouble once agin has to do a lot with the exhaust valve/port/header. if the engine is short on exhaust flow at the top of the rpm range you can be sure opening the valve too soon there will show no gain up there. In the midrange and where the header is working ok there probably won't be any disadvanage to it. On an engine with a plenum intake early IO (and overlap in general) can really screw up the idle and part throttle perfomance, but we run IR carbs so no problem with that unless the header is causing it.

Both these things together gives you more overlap total. If the header is working well at X rpms then more overlap can be a good thing at X rpms. If the header is up to no good at Y rpms, then it can hurt perfomance in some way at Y rpms.
if you have very little or no overlap(like the stock cam) the header is not very important, it can't hurt or help much. If you run lots of overlap the header can make or break the way it runs; like what kind of header you use determines the nature of the beast!
If the exhaust is limited at the top of the rpm range then you'd probably want to move the whole overlap period later(like retarding the cam). if the exhaust is a little on the big side compared to the rest of the engine than you'd want to move the whole overlap period sooner to help prevent any kind of reversion and get it "on the cam" sooner.

That.....is the overlap. open it up and you'll find out what is happening at the snap between the exhaust and intake stroke, big overlap allows the header and intake to play with each other for better or worse.